It depends on what kind of working out you are doing and what your goal is. For aerobic activity, it's best to fast for an hour or so before... maybe have a small snack like carrots or hard boiled eggs (something with low carb content) so you're not hungry while you work out. That will help your body burn fat instead of carbs. Then eat something afterward... light, of course.
If you are lifting weights, you will want to eat somehting with a decent amount of carbs about an hour before hand so you have the energy and stamina to work hard, and eating something high in protein immediately afterward helps build the muscles (I found a protein shakes work best in this capacity. Easier to carry around than a lunchbox full of eggs, too).